Not so simple, not so subtle: the interspecies competition between and and its impact on the evolution of biofilms.

biofilms have a fundamental role in shaping the soil ecosystem. During this process, they unavoidably interact with neighbour bacterial species. We studied the interspecies interactions between biofilms of the soil-residing bacteria and related species. We found that proximity between the biofilms triggered recruitment of motile cells, which engulfed the competing colony. Upon interaction, secreted surfactin and cannibalism toxins, at concentrations that were inert to itself, which eliminated the colony, as well as colonies of . Surfactin toxicity was correlated with the presence of short carbon-tail length isomers, and synergistic with the cannibalism toxins. Importantly, during biofilm development and interspecies interactions a subpopulation in biofilm lost its native plasmid, leading to increased virulence against the competing species. Overall, these findings indicate that genetic programs and traits that have little effect on biofilm development when each species is grown in isolation have a dramatic impact when different bacterial species interact.